There are several production methods of metal matrix composites. One of the more economical ways is to combine ceramic reinforcement with molten metallic alloy by mixing action or by infiltration. Incorporation of ceramic particles in aluminum alloys can give composite materials with a reinforcement content practically up to about 20 vol.%. Even by using semi-solid processes, the particle content over 30 vol.% can not thus far be achieved due to the high viscosity of the semi-solid alloy with added particles. In applications where the coefficient of thermal expansion should be minimal, as for electronic packaging, the aluminum composites with 25 vol. % of reinforcement cannot match the coefficient of ceramic materials used as substrates in electronic circuits. Composites with a higher reinforcement content could be made by conventional powder metallurgy but the shapes available by this technology are quite limited.
To produce complex-shaped parts made of metals and/or ceramics, recent developments in powder injection molding and mold transfer technologies have made it possible to obtain near-net-shape parts of advanced materials at a significant production level. The powder injection molding step is carried out with a conventional equipment used in the polymer industry, employing a binder, usually a low-melting polymeric substance such as a wax. Before sintering the so-called green part, the binder has to be removed from the part. Various methods have been investigated to that effect but very few have been found efficient in terms of processing time (Lange et al, P/M Injection Molding Technique for Ceramic and Metal Parts, Powder Met. Int., 18 (6), 416-421, 1986 and Zhang et al, Powder Injection Molding of 17-4PH Stainless Steel, Proceedings of the Powder Injection Molding Symposium 1992, June 21-26, San Francisco, P.H. Booker, J. Gaspervich and R.M. German (eds.), American Powder Metallurgy Institute, 219-227). The binder removal methods suggested so far are: solvent extraction, thermal evaporation or degradation, and wicking (Aria et al, Influence of Process Variables on Debinding by Melt Wicking, Conference: Modern Developments in Powder Metallurgy. Vol. 18, Orlando, FLA, 403-416, 5-10 June 1988). The duration of these prior art debinding steps varies from about 2 to about 20 hours.
It should be noted that the fabrication of aluminum matrix composites with high reinforcement content by injection molding is not an easy task due to the oxide layer covering the aluminum powder. The packing pressure involved in the molding equipment is just high enough to cause the deformation of aluminum particles that facilitates sintering. When ceramic particles are added, the pressure is not sufficient to fill the gaps between the reinforcement particles because the wetting of the alloy on the ceramic is very poor.